Engine controllers and engine control strategies operate fuel injectors to deliver precise amounts of fuel at precise times relative to engine crankshaft angle to improve engine efficiency and reduce engine emissions. Further, when precise amounts of fuel are injected at a precise engine crankshaft angle, an expected amount of torque may be produced at the engine crankshaft via the engine cylinder. However, if a fuel injector or other component of a fuel injection system degrades, it is possible for engine torque and emissions to degrade during engine operation. For example, a change of injector response time may degrade fuel injection timing and amount of fuel injected so that engine torque varies and engine emissions degrade.
In U.S. Pat. No. 7,317,983 the inventors describe a method for balancing cylinder torque in response to engine speed. In particular, the method appears to adjust an amount of fuel injected to a cylinder based on engine speed that is related to a particular fuel injection and combustion event. However, the method appears to correct for torque imbalance without diagnosing injector operation. For example, the method appears to adjust an amount of fuel injected to a cylinder to correct a torque imbalance, but the method does not appear to determine whether or not the fuel injector is operating within expected performance criteria. Nor does the method appear to diagnose whether fuel injection errors are related specifically to variation of injected fuel amount or variation of start or end of fuel injection.
The inventors herein have recognized the above-mentioned shortcomings and have developed a method for diagnosing fuel injection, comprising: adjusting an amount of fuel injected to a cylinder to balance a torque produced via the cylinder with a torque produced via a different cylinder; sweeping fuel injection timing of the cylinder during the adjusting of the fuel injection amount; and indicating degradation of fuel injection when a minimum amount of fuel injected to the cylinder to balance the torque produced via the cylinder is outside a range.
By adjusting fuel amount and fuel injection timing it may be possible to determine whether a fuel injector is injecting fuel in an expected amount during an expected time period. For example, sweeping injected fuel amount and fuel injection timing can provide data for determining where a minimum amount of fuel injected balances cylinder torque. The amount of the minimum amount of fuel to balance cylinder torque and the timing where the minimum amount of fuel that balances cylinder torque occurs can be compared to timing and amount of a previously determined minimum fuel injected to balance cylinder torque. If the presently determined minimum amount of fuel to balance torque of an engine cylinder is outside of a range, injector degradation may be indicated. In this way, cylinder torque balancing and the minimum amount of fuel injected to balance torque of a cylinder can be used to diagnose operation of a fuel injector.
The present description may provide several advantages. For example, the approach may provide specific information regarding fuel injector degradation. For example, the approach can isolate whether injector degradation is related to an amount of fuel injected or to a timing of start or end of fuel injection. Further, the approach may be applied without additional diagnostic hardware. Further still, the approach may be applied at conditions where the engine operates during the normal course of operation.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.